HEK 293 cells

Human embryonic kidney 293 cells, also often referred to as HEK 293, HEK-293, 293 cells, or less precisely as HEK cells, are a specific immortalised cell line originally derived from human embryonic kidney cells grown in tissue culture taken from a female fetus.^[1] HEK 293 cells have been widely used in cell biology research for many years, because of their reliable growth and propensity for transfection. They are also used by the biotechnology industry to produce therapeutic proteins and viruses for gene therapy.

History[]

293FT cells, a variation of 293 cell

HEK 293 cells were generated in 1973 by transfection of cultures of normal human embryonic kidney cells with sheared adenovirus 5 DNA in Alex van der Eb's laboratory in Leiden, the Netherlands. The cells were obtained from a single, aborted or miscarried fetus, the precise origin of which is unclear.^[2][3] The cells were cultured by van der Eb; the transduction by adenovirus was performed by Frank Graham, a post-doc in van der Eb's lab. They were published in 1977 after Graham left Leiden for McMaster University.^[4] They are called HEK since they originated in human embryonic kidney cultures, while the number 293 came from Graham's habit of numbering his experiments; the original HEK 293 cell clone was from his 293rd experiment. Graham performed the transfection a total of eight times, obtaining just one clone of cells that were cultured for several months. After presumably adapting to tissue culture, cells from this clone developed into the relatively stable HEK 293 line.

Subsequent analysis has shown that the transformation was brought about by inserting ~4.5 kilobases from the left arm of the viral genome, which became incorporated into human chromosome 19.^[5]

For many years it was assumed that HEK 293 cells were generated by transformation of either a fibroblastic, endothelial or epithelial cell, all of which are abundant in kidneys. However, the original adenovirus transformation was inefficient, suggesting that the cell that finally produced the HEK 293 line may have been unusual in some fashion. Graham and coworkers provided evidence that HEK 293 cells and other human cell lines generated by adenovirus transformation of human embryonic kidney cells have many properties of immature neurons, suggesting that the adenovirus preferentially transformed a neuronal lineage cell in the original kidney culture.^[6]

A comprehensive study of the genomes and transcriptomes of HEK 293 and five derivative cell lines compared the HEK 293 transcriptome with that of human kidney, adrenal, pituitary and central nervous tissue.^[7] The HEK 293 pattern most closely resembled that of adrenal cells, which have many neuronal properties. Given the location of the adrenal gland (adrenal means "next to the kidney"), a few adrenal cells could plausibly have appeared in an embryonic kidney derived culture, and could be preferentially transformed by adenovirus. Adenoviruses transform neuronal lineage cells much more efficiently than typical human kidney epithelial cells.^[6] An embryonic adrenal precursor cell therefore seems the most likely origin cell of the HEK 293 line. As a consequence, HEK 293 cells should not be used as an in vitro model of typical kidney cells.

HEK 293 cells have a complex karyotype, exhibiting two or more copies of each chromosome and with a modal chromosome number of 64. They are described as hypotriploid, containing less than three times the number of chromosomes of a haploid human gamete. Chromosomal abnormalities include a total of three copies of the X chromosomes and four copies of chromosome 17 and chromosome 22.^[7][8] The presence of multiple X chromosomes and the lack of any trace of Y chromosome derived sequence suggest that the source fetus was female.

Variants[]

Multiple variants of HEK 293 have been reported.^{[citation needed]}

Applications[]

Immunofluorescent HEK 293 cells

HEK 293 cells are straightforward to grow in culture and to transfect. They have been used as hosts for gene expression. Typically, these experiments involve transfecting in a gene (or combination of genes) of interest, and then analyzing the expressed protein. The widespread use of this cell line is due to its transfectability by the various techniques, including calcium phosphate method, achieving efficiencies approaching 100%.

Examples of such experiments include:

• Effects of a drug on sodium channels^[10]
• Inducible RNA interference system^[11]
• Isoform-selective protein kinase C agonist^[12]
• Interaction between two proteins^[13]
• Nuclear export signal in a protein^[14]

HEK 293 cells were adapted to grow in suspension culture, as opposed to proliferation on plastic plates, in 1985.^[15] This enabled the growth of large amounts of recombinant adenovirus vectors.

A more specific use of HEK 293 cells is in the propagation of adenoviral vectors.^[16] Viruses offer an efficient means of delivering genes into cells, which they evolved to do, and are thus of great use as experimental tools. However, as pathogens, they also present a risk to the experimenter. This danger can be avoided by the use of viruses which lack key genes, and which are thus unable to replicate after entering a cell. In order to propagate such viral vectors, a cell line that expresses the missing genes is required. Since HEK 293 cells express a number of adenoviral genes, they can be used to propagate adenoviral vectors in which these genes (typically, E1 and E3) are deleted, such as AdEasy.^[17] However, homologous recombination between the inserted cellular Ad5 sequence and the vector sequence, although rare, can restore the replication capacity to the vector.^[18]

An important variant of this cell line is the 293T cell line. It contains the SV40 large T-antigen that allows for episomal replication of transfected plasmids containing the SV40 origin of replication. This allows for amplification of transfected plasmids and extended temporal expression of desired gene products. HEK 293, and especially HEK 293T, cells are commonly used for the production of various retroviral vectors.^[19] Various retroviral packaging cell lines are also based on these cells.

Native proteins of interest[]

Depending on various conditions, the gene expression of HEK 293 cells may vary. The following proteins of interest (among many others) are commonly found in untreated HEK 293 cells:

• Corticotrophin releasing factor type 1 receptor^[20]
• Sphingosine-1-phosphate receptors EDG1, EDG3 and EDG5^[21]
• Muscarinic acetylcholine receptor M3^[22]
• Transient receptor potential TRPC1, TRPC3, TRPC4, TRPC6^[23]

Bioethics[]

Alvin Wong argues that despite the uncertainty over the origin of the fetus used to obtain the cell line, circumstantial evidence strongly suggests that it came from an elective abortion. In the context of Catholic teaching, this presents ethical difficulties for using HEK 293 and derivative products, such as vaccines.^[24][25]

On 21 December 2020, the Congregation for the Doctrine of the Faith, with the document receiving approval from the Pope, have stated that “it is morally acceptable to receive COVID-19 vaccines that have used cell lines from aborted fetuses in their research and production process”, but only where other alternatives are non-existent (or currently unavailable), or when there's the risk of a worse danger.^[26]

During the COVID-19 pandemic, anti-vaccination activists noted that HEK 293 cells are used in the manufacturing of the Oxford–AstraZeneca COVID-19 vaccine (AKA AZD1222). The cells are filtered out of the final products.^[27][25]

References[]

External links[]

Wikimedia Commons has media related to HEK293 cells.

• HEK 293 Transfection and Selection Data @ Cell-culture Database
• A HEK293 Cell Database
• 293 Cells (CRL-1573) in the ATCC database
• Transcript of FDA meeting, in which, starting page 77, van der Eb describes in detail the origin of HEK 293 cell
• 293T in the Culture Collections of Public Health England
• Cellosaurus entry for HEK 293